Question

From which latin word , the english word 'city' comes ?

Answer 1

The sense has been transferred from the inhabitants to the place. The Latin word for "city" was urbs, but a resident was civis.

Answer 2

Urbs indicates a fully evolved city, as does civitas, though the former has more to do with the physical infrastructure and the latter invokes the community aspect of the city.   

Oppidum and astu imply something smaller, like a town.  

Arx indicates a fortification, and, by metonymy, moenia ('walls') can mean a walled town or fortification.  

Vicus usually implies a smaller village.